Enhance interlinking of the three lobid services

[acka47]

This is a superissue for different tasks we partly already have tickets for:

• Add links from GND entitites to lobid-resources: Add links from GND entitites to lobid-resources lobid-gnd#38
• Add GND links to lobid-organisations: Add GND links lobid-organisations#361
• Add search box in lobid-organisations for libraries we have holdings in lobid-resources: Add search box for libraries we have holdings in lobid-resources lobid-organisations#397
• Furthermore, @dr0i recently suggested to link to lobid-gnd instead to the DNB catalog when in lobid-resources clicking on the link symbol besides a person, corporate body or subject heading.